Medical devices are known for thermally treating tissue on the exterior and the interior of the body. One category of such devices is the minimally-invasive, catheter-based device that is introduced into the vasculature. One feature of these devices is the means by which the device is positioned at the treatment site. For example, some devices are actively steered through the vasculature using a steering or deflection mechanism, such as a pull-wire; whereas other devices are introduced over a wire that has already been guided to a selected location, wherein the wire acts as a guide that leads the device to the treatment site. Although a device can be configured so that the guiding wire is substantially external to the device, most known devices include a central longitudinal lumen that receives the wire.
Another feature of the minimally-invasive, catheter-based, thermal-treatment device is the thermal treatment mechanism. One category of devices thermally treats tissue by cooling it, wherein cooling is effected by injecting coolant into a portion of the device, such as a distal device portion that has advantageous thermal transfer properties, and placing the distal device portion near or in contact with the tissue. The distal end portion can have a fixed diameter that is substantially the same as the diameter of the remainder of the catheter or it can have a variable diameter, such as is provided by a balloon. However, regardless of whether the distal end portion is of fixed or variable diameter, the overall size of the device and the injection tube are limited by the dimensions of the vasculature. Typical devices are 2 mm to 4 mm in diameter. Given the small device size, it has proven challenging to cool or freeze warm bodily tissue to a temperature near or well below freezing. Accordingly, it is important to maximize the cooling potential of a particular coolant or refrigerant by delivering or injecting it at a particular location within the device.
In order to cool a treatment segment at a distal end of a device having an expanded or larger surface area than the device body, for example, effective cooling may be achieved by either uniformly spraying or dispersing refrigerant onto the expanded surface of the treatment segment, or by flooding the treatment segment with a refrigerant. Flooding a treatment segment may require larger volumes of coolant, resulting in inefficient use and increased costs, making the substantially uniform spraying or dispersion of coolant an attractive alternative. Devices as depicted in U.S. Pat. No. 6,235,019 provide multiple coolant injection tubes. Alternatively, as shown in U.S. Pat. No. 5,899,898, a single injection tube can be provided with openings along its length. Although such coolant injection structures can be very desirable for creating an elongated cooling zone, they are less suitable for balloon devices or over-the-wire devices. With respect to an over-the-wire device, it will be noted that a relatively large central passage for the wire actually blocks or isolates the injection lying at one side of the passage from the opposite side of the passage, thereby insulating the masked side of the device and creating uneven cooling.
Although not directed to issues related to an over-the-wire device, U.S. Pat. No. 6,551,274 illustrates a loosely coiled injection tube. However, as with the linear injection tubes having a series of longitudinal ports, at regular intervals along the device, the central structure masks the injection tube.
In view of the preceding, it is believed that an improved injection tube would be desirable for use with over-the-wire devices or other devices that have structures other than an injection tube in the cooling chamber of the device.